Map of the galactic center region in the 1.8 MeV 26Al gamma-ray line

A map of the galactic center region in the 1.8 MeV gamma-ray line from radioactive Al²⁶ was derived from balloon flight data of the MPI Compton telescope. The image of the observed region of the sky is consistent with a point source origin at l = 1° ± 4°, b = −30 ± 4°. Diffuse emission models from unresolved candidate sources like supernovae, novae, Wolf-Rayet stars, and massive stars fit our data worse than a point source, but cannot be rejected definitely.     

A high sensitivity phoswich scintillator X-ray telescope for hard X-ray (20 – 120 keV) astronomy from balloon platform

A large area (400 cm²) low background X-ray telescope consisting of four collimated NaI/CsI scintillator phoswich detectors (each 100 cm²) was built and successfully flown several times during 1980–1984. The phoswich configuration enables one to eliminate X-ray background produced by high energy atmospheric and cosmic gamma-rays. Combined with large area, small field of view (5° × 5°) and large exposure time that was possible due to an on-board telescope pointing programmer, for the 20 – 120 Kev energy range, 3σ sensitivity achieved was 5 × 10⁻⁶ photon/cm² sec Kev for exposure time of 10⁴ sec at observational altitude of 4 g/cm². The Instrument characteristics, relevant details on pointing system, detector system, associated electronics and telemetry and in-flight performance in 1983 and 1984 are presented.     

The position sensitive low energy detector on board the ZEBRA telescope

In order to improve the low energy capability (15 ÷ 150 KeV) of the balloon borne “ZEBRA” low energy gamma imaging telescope (150 KeV-20 MeV), a large area, high spectral resolution (5% at 60 KeV), low background detector has been designed and is now under development.It consists of two MultiWire Spectroscopic Proportional Counter (SPC), escape gated, that have a sensitive area of 6000 cm², and are placed above the large area array of sodiumiodide position sensitive elements.     

The oriented scintillation spectrometer experiment for the gamma-ray observatory

The Oriented Scintillation Spectrometer Experiment (OSSE) for the Gamma Ray Observatory is described. OSSE uses four identical NaI(T1)-CsI(Na) phoswich detectors to provide gamma-ray line and continuum detection capability in the 0.05–10 MeV energy range. Additional gamma-ray and neutron detection capability is achieved above 10 MeV. Each detector has a CsI annular shield and a tungsten alloy collimator which define a 5° × 11° (FWHM) field-of-view. The detectors have independent, single-axis orientation systems which permit offset pointing to provide source-background subtraction. The sensitivity for line gamma rays in the 0.05–10 MeV region will be 2–3 × 10^?5 photons/cm²-s for a 10⁶-second observation period. The several modes of data acquisition and the emphases for the planned observational program are discussed.     

Hard X-ray observation of galactic X-ray sources

A large (1455 cm²) hard X-ray telescope was successfully launched aboard a stratospheric balloon on October 4, 1980. During this flight four galactic X-ray sources were observed, namely the transient recurrent X-ray pulsar A0535+26, the Crab Nebula, Cygnus X-1 and X Persei. Here we report the results on the latter two sources. From Cygnus X-1 we measured a photon flux in the band 30 to 200 keV, of 3.5 × 10^?2 photons cm^?2 which is 6.5 times lower than that recieved from the source in a “low” intensity state in the same energy band. In addition, the photon spectrum in the same energy band was very soft and consistent with a power law with photon index α = 2.71 ± 0.14. Even if a simultaneous observation of the source at lower energies was not available, our data strongly suggest that we observed the source during a “high” intensity state. We report also positive detection in the band 30 to 200 keV of the low luminosity X-ray pulsar X Persei. In its spectrum we confirm the presence of a hard X-ray tail consistent with a power law (photon index α = 2.17 ± 0.42).     

An imaging telescope for soft gamma-ray astronomy: The preliminary in-flight tests

A large area (6000 cm²) actively shielded low energy gamma-ray telescope is going to be built by an Anglo-Italian collaboration. The telescope, named ZEBRA, will be capable of producing images of the X and gamma ray sky in the energy range 0.015–20 MeV with an intrinsic angular resolution of a few tenths of a degree. A prototype detector has been built in order to experimentally study the main characteristics of the detection plane. The preliminary results obtained during a balloon flight from Trapani, Sicily in July 1981 are presented.     

Guidance and control of a balloon-borne X-ray telescope with onboard and ground based computers

The balloon payload HEXE ^A) is designed to observe cosmic X-ray sources in the energy range 20–250 keV. Its detectors are ‘Phoswich’ scintillators with a total sensitive area of 2300 cm² and a cooled Ge solid state detector with an area of 100 cm² [1]. The instrument was flown successfully in 1980 and 1981 from Palestine, Texas.Here we describe the control of the instrument and guidance of the telescope as well as the method of data retrieval and real time analysis. These tasks are performed by a ground based minicomputer (HP 1000) and onboard microprocessors (M 6800) which are linked together by data and command telemetry.     

Fabrication and flight performance of a large area balloon borne hard X-ray telescope

We describe the fabrication and flight performance of a balloon-borne large area hard X-ray (20–100 keV) telescope for spectral studies of discrete cosmic X-ray sources. The telescope consists of two multi-wire Xenon filled proportional counters of effective area 1200 cm² each, mounted on an orientable platform. It can be pre-programmed to track any celestial source with a pointing accuracy of 0.5 degrees. For one hour of observation the telescope has a 5 σ detection sensitivity of 10⁻⁵ ph cm⁻² s⁻¹. The laboratory test results and the performance in a series of balloon flights conducted in 1984–1986 period is discussed and the preliminary results obtained for some X-ray sources are presented.     

The ROSAT mission

A primary scientific objective of the ROSAT mission is to perform the first all-sky survey with an imaging X-ray telescope leading to an improvement in sensitivity by several orders of magnitude compared with previous surveys. A large number of new sources (? 10⁵) will be discovered and located with an accuracy of 1 arcmin or better. These will comprise almost all astronomical objects from nearby normal stars to distant quasistellar objects. After completion of the survey which will take half a year the instrument will be used for detailed observations of selected sources with respect to spatial structure, spectra and time variability. In this mode which will be open for guest observers ROSAT will provide substantial improvement over the imaging instruments of the Einstein observatory.The main ROSAT telescope consists of a fourfold nested mirror system with 83 cm aperture having three focal plane instruments. Two of them will be imaging proportional counters (0.1 – 2 keV) providing a field of view of 2°, an angular resolution of ≈ 30″ in the pointing mode and a spectral resolution ^ΔE/E ≈ 45% FWHM at 1 keV. The third focal instrument will be a high resolution imager (≈ 3″). The main ROSAT telescope will be complemented by a parallel looking Wide Field camera which extend the spectral coverage into the XUV band.     

Simulation experiments of the cosmic ray isotope telescope on ETS VI

A computer simulation was carried out to evaluate the basic characteristics of a Δ E×E cosmic ray telescope consisting of 23 solid state detectors including 3 position sensitive detectors with large effective area. Based on the simulation, the geometric factor of the telescope is deduced to be as large as 22.5 cm²sr, almost independent of charge and energy concerned. The energy ranges to be covered by the telescope are, for example, 18–98 MeV/n for Li and 56–339 MeV/n for Fe. By analyzing simulated data, the mass resolution for iron in the overall energy range covered by the telescope is estimated as about 0.22 amu in standard deviation. The expected counting rates and mass-histograms are simulated for Galactic cosmic rays and solar energetic particles.     

First calibration measurements with the dust impact detector DIDSY-IPM

The IPM detector consists of two separate impact ionization detectors, one of them covered by a 2.5 μm thick plastic film and a piezoelectric sensor mounted to the back of the joint impact plate. First impact tests, with iron projectiles in the mass range 10^?15 to 10^?9 g and in the speed range 1 km/s to 70 km/s, were performed with the calibration (FS) and the flight (F) model of this detector. The charge yield at 69 km/s impact speed (flyby speed of GIOTTO) has been extrapolated from the data and amounts to 400 Coulombs per gram. This corresponds to a preliminary sensitivity threshold for the impact ionization detector of about 6×10^?17 g. The penetration limit introduced by the plastic film is about 10^?14 g for iron particles. Only the biggest particles used for the test produced signals at the piezoelectric sensor. If one assumes an energy dependence of the piozoelectric signal, a preliminary sensitivity threshold of about 10^?13 g at 69 km/s can be established.     

Hadamard X-ray Spectro-telescope

The Hadamard X-ray Spectro-telescope consists of a flat Bragg crystal, an Hadamard mask and an imaging proportional counter. We have achieved α??α≈50, which is limited by the position resolution of the detector. This telescope is useful to observe the spectral structure of extended X-ray sources. We introduce a new type of read out method (Grouped Wire Method) for the position sensitive proportional counter in order to get high energy and position resolutions for the Hadamard Spectro-telescope. In principle, this method is capable of obtaining the desired linearity over the whole area of the detector.     

Equatorial secondary cosmic ray observatory to study space weather and terrestrial events

Recently, equatorial secondary cosmic ray observatory has been established at Equatorial Geophysical Research Laboratory (EGRL), Tirunelveli, (Geographic Coordinates: 8.71°N, 77.76°E), to study secondary cosmic rays (SCR) produced due to the interaction of primary cosmic rays with the Earth’s atmosphere. EGRL is a regional center of Indian Institute of Geomagnetism (IIG), located near the equator in the Southern part of India. Two NaI(Tl) scintillation detectors are installed inside the temperature controlled environment. One detector is cylindrical in shape of size 7.62?cm?×?7.62?cm and another one is rectangular cuboid of 10.16?cm?×?10.16?cm?×?40.64?cm size. Besides NaI(Tl) detectors, various other research facilities such as the Geomagnetic observatory, Medium Frequency Radar System, Digital Ionosonde, All-sky airglow imager, Atmospheric electricity laboratory to measure the near-Earth atmospheric electric fields are also available at EGRL. With the accessibility of multi- instrument facilities, the objective is set to understand the relationship between SCR and various atmospheric and ionospheric processes, during space weather and terrestrial events.For gamma-ray spectroscopy, it is important to test the performance of the NaI(Tl) scintillation detectors and to calibrate the gamma-ray spectrum in terms of energy. The present article describes the details of the experimental setup installed near the equator to study cosmic rays, along with the performance testing and calibration of the detectors under various conditions. A systematic shift in the gain is observed with varying temperature of the detector system. It is found that the detector’s response to the variations in the temperature is not just linear or non-linear type, but it depends on the history of the variation, indicating temperature hysteresis effects on NaI detector and PMT system. This signifies the importance of isothermal environment while studying SCR flux using NaI(Tl) detectors, especially for the experiments conducted during daytime such as solar eclipses etc.     

The extreme ultraviolet explorer and the local interstellar medium

The Extreme Ultraviolet Explorer (EUVE) mission is described with emphasis on the overall capabilities of the instrumentation and the relevance of the mission to determining parameters of the local interstellar medium. The primary purpose of the mission is to search the celestial sphere for astronomical sources of extreme ultraviolet (EUV) radiation (100–1000Å). The search will be accomplished with the use of three EUV telescopes, sensitive to different segments of the EUV band. A fourth telescope will perform a high sensitivity search of a limited sample of the sky in the shortest wavelength bands. The all-sky survey will be carried out in the first six months of the mission. The second six months of the mission, conducted entirely by Guest Investigators selected by NASA, will be devoted to spectroscopic observations of selected EUV sources. The instrumentation is now well developed. The mirrors meet the requirements of the mission with the best mirror having a full-width half energy spread of 8 arc seconds and a surface finish of 20Å. Prototype thin film bandpass filters have been flown on the Space Shuttle and their performance optimized. Prototype detectors have been developed which have 600 by 600 pixel imaging capability and up to 80% quantum efficiency in parts of the EUV band. A newly invented, high efficiency, grazing incidence spectrometer using variable line space gratings is under development; prototype gratings have been fabricated which provide 75% of theoretical efficiency. An end-to-end (star to as-received flight data) model of the mission has been constructed. Hypothetical, but realistic, flux data from continuous astronomical sources absorbed by intervening material have been processed through this model and show the ability of the EUVE instrumentation to measure such parameters as the hydrogen to helium ratio of the local interstellar medium.     

Gamma-ray burst detection capabilities of comptel

The imaging gamma-ray telescope COMPTEL, capable of detecting gamma rays in the 1 to 30 MeV range, is one of four experiments onboard NASA's Gamma-Ray Observatory GRO. Besides its primary objectives COMPTEL will contribute to the understanding of cosmic gamma-ray bursts. Summarising, COMPTEL localises bursts (S (E > 1 MeV) ≥ 2.10⁻⁶ erg/cm²) within 1 sr FOV to better than 1° at medium gamma-ray energies, measures continuum energy spectra in the range 0.1 MeV to 20 MeV with fluence S ≥ 6.9 10⁻⁷ erg/cm² (5σ, E≥100 keV), measures gamma-ray lines with detector resolution 9.6% (at 0.5 MeV) and 7.0% (at 1.5 MeV) and determines time histories of both gamma-ray line and continuum emission with t ≥ 0.1 sec resolution.     

Measurements of the earth radiation budget from satellites during the first garp global experiment

Two special measurements of the energy exchange between earth and space were made in connection with the FGGE. A global monitoring program using wide-field-of-view and scanner detectors from NASA's NIMBUS-7 satellite successfully returned measurements during the entire FGGE. This experiment system also used a black cavity detector to measure the total energy output of the sun to very high precision. A second set of high frequency time and space estimates of the radiation budget were determined from selected geostationary satellite data. Preliminary results from both radiation budget data sets and the solar “constant” measurements will be presented.     

First measurements of cosmic-ray nuclei at high energy with CREAM

The balloon-borne cosmic-ray experiment CREAM-I (Cosmic-Ray Energetics And Mass) recently completed a successful 42-day flight during the 2004–2005 NASA/NSF/NSBF Antarctic expedition. CREAM-I combines an imaging calorimeter with charge detectors and a precision transition radiation detector (TRD). The TRD component of CREAM-I is targeted at measuring the energy of cosmic-ray particles with charges greater than Z ∼ 3. A central science goal of this effort is the determination of the ratio of secondary to primary nuclei at high energy. This measurement is crucial for the reconstruction of the propagation history of cosmic rays, and consequently for the determination of their source spectra. First scientific results from this instrument are presented.     

The low energy gamma-ray experiments on GRO in perspective

The NASA Gamma-Ray Observatory, GRO, will carry two instruments for low energy gamma-ray astronomy. The ‘Oriented Scintillation Spectrometer Experiment - OSSE’ represents the latest step in the evolution of collimated detectors. A large detection area, simultaneous source and background observation and rigorous control over systematic errors yield significant improvements in sensitivity over earlier instruments. The ‘Imaging Compton Telescope - COMPTEL’ brings the proven concept of the Compton telescope to the state of the art level. Position sensitive scintillation detectors make it possible to generate sky images with a resolution of about 2° over a f.o.v. of about 1 sr. The complementary nature of these two experiments promises a first in-depth exploration of the sky in a wavelength range which covers the transition from the X-ray sky to the apparently unrelated high energy gamma-ray sky. Possible directions of further evolution of these experiments will be discussed.     

An imaging telescope for soft gamma ray astronomy

A telescope capable of producing images of the gamma ray sky in the energy range 0.2–20 MeV with an angular resolution of a few tenths of a degree is presented. This capability is achieved by means of a large array of Sodium Iodide position sensitive elements together with a coded imaging mask. The expected performance, derived from calculations and preliminary laboratory tests, is described.